Blasting machine with overvoltage and undervoltage protection for the energy storage capacitor

ABSTRACT

A blasting machine for firing an explosive bridge wire device or the like. The blasting machine includes a storage capacitor that is charged to an energy level within a predetermined range. The upper limit of the energy range is controlled by a two-electrode spark discharge device which operates as an upper voltage control and the lower limit of the energy range is controlled by a twoelectrode spark device which does not permit the capacitor to be discharged until the second device is conducting, which occurs at the desired lower voltage level whereby the energy discharged from the storage capacitor must be within the energy levels established by the two spark discharge devices.

United States Patent [191 Phinney et a1. 5]March 20, 197 3 [5 BLASTINGMACHINE WITH 3,417,306 12/1968 Knak ..320/1 OVERVOLTAGE AND UNDERVOLTAGEPROTECTION FOR THE ENERGY STORAGE CAPACITOR Primary Examiner--BemardKonick Assistant Examiner-Stuart Hecker Attorney-Raymond J. Eifler eta1.

[75] Inventors: Earl M. Phinney, Oneonta; Irving E.

Linkroum, Hancock, both of N.Y. [57] ABSTRACT 73 A Th sslgnee BendCorporahon Southfield A blasting machine for firing an explosive bridgewire MlCl'l. device or the like. The blasting machine includes a [22]Filed: Nov. 23, 1971 storage capacitor that is charged to an energylevel [211 App]; No: 201,527 within a predetermined range. The upperlimit of the energy range is controlled by a two-electrode sparkdischarge device which operates as an upper voltage US. Cl- ..320/1, 3control and the lower of the energy range is con- [51] Int. Cl. ..H03k3/30, H02m 3/22 trolled by a two electrode Spark device which does not[58] Field of Search ..320/l; 317/80; 307/108 permit the capacitor to bedischarged until the Second 56 device is conducting, which occurs at thedesired 1 References C'ted lower voltage level whereby the energydischarged UNITED STATES PATENTS from the storage capacitor must bewithin the energy levels established by the two spark discharge devices.3,541,393 11/1970 Diswood ..320/1 X 2,826,693 3/1958 Resnik ..320/l X 2Claims, 2 Drawing Figures CAPACITOR v CHARGE 8 VOLTAGE D HA s INDICATOR6 I] 3) FIRING CIRCUIT POWER ENERGY PULSE SUPPLY STORAGE GENERATORTRIGGER LOAD 2 VOLTAGE m R EG U LATOR PATENTEDMAR20|973 SHEET 20F 2 NMEDQE BLASTING MACHINE WITH OVERVOLTAGE AND UNDERVOLTAGE PROTECTION FORTHE ENERGY STORAGE CAPACITOR BACKGROUND OF THE INVENTION This inventionrelates to an improved blasting machine for detonating blasting caps orthe like. The invention is more particularly related to a batterypowered blasting machine of the capacitor discharge type.

Basically, electrical systems for firing explosive devices include asource of power such as a battery, an oscillator, a transformerresponsive to the oscillator for stepping up the pulses therefrom, astorage capacitor which is charged by the pulses from the transformer,and a trigger circuit which allows the energy stored in the capacitor todischarge to fire an explosive device. The energy stored in thecapacitor is discharged through the explosive device by means of atriggering circuit which may be operated automatically or manually.Examples of such blasting devices may be found in US. Pat. No. 3,417,306entitled Regulated woltage Capacitor Discharge Circuit to J .'L. Knak,issued Dec. 17, 1968, and US. Pat. No. 3,275,884 entitled ElectricalApparatus for Generating Current Pulses to L. H. Segall et al., issuedSept. 27, 1966.

In certain blasting operations such as those performed in tunnels andshaft mining, it may be necessary to connect from as few as one blastingcap and as many as 150 blasting caps together in a parallel circuit.Parallel connections are used because such connections permit rapidconnection of the blasting caps with minimal possibility of error. Toinsure that all the blasting caps are fired, the blasting machine mustalways deliver a given minimum energy each time it is fired, otherwiseall of the blasting caps may not be fired. Further, it is also importantthat the blasting machine does not deliver too much energy to theblasting caps, otherwise malfunction of some of the blasting caps mayoccur. Therefore, to insure that all blasting caps are fired theblasting machine must always deliver an amount of energy in apredetermined energy range depending upon the number of blasting caps tobe fired.

SUMMARY OF THE INVENTION This invention prevents the firing of ablasting machine below and above a predetermined energy range.

The invention is a battery powered blasting machine characterized by anelectrical circuit that charges a storage capacitor within apredetermined energy range before it can be discharged. The circuit isfurther characterized by two, two electrode spark discharge devices, oneof which establishes the upper energy level and the other of whichestablishes the lower energy level.

In one embodiment of the invention, the blasting machine comprises: acapacitor; means for supplying electrical energy to the capacitor; meansfor producing a plurality of electrical pulses when the capacitor hasreached a first predetermined energy level, the pulse means including asecond normally nonconductive gaseous conductor which is renderedconductive when a predetermined voltage is applied thereto and aresistor-capacitor circuit in series with the second gaseous conductorso that when the second gaseous con ductor is rendered conductive, thecapacitor in series with the resistor lowers the voltage applied to thesecond gaseous conductor to a voltage below the predetermined value andthe second gaseous conductor is rendered nonconductive; switching meansfor receiving the pulses, the switching means ,operable to permit thedischarge of the capacitor only during the presence of the pulses,whereby the capacitor cannot be discharged below the predeterminedenergy level, the switching means including a first normallynonconductive gaseous conductor in circuit relationship with the pulsemeans, thefirst gaseous conductor being rendered conductive uponreceiving the pulses whereby when pulses from the pulse means aretransmitted to the first gaseous conductor, the first gaseous conductoris rendered conductive to permit the capacitor to discharge, and aswitch connected between the first gaseous conductor and the pulsemeans, the switch operable in the ON position to permit the passage ofsaid pulses to the first gaseous conductor whereby the capacitor isdischarged only when the switch is in the ON position and when the pulsemeans is producing pulses; and a third gaseous conductor means forpreventing the capacitor from exceeding a second predetermined energylevel which is above the first predetermined energy level whereby thecapacitor is prevented from reaching energy levels above the secondpredetermined energy which may cause failure of said means for storingelectrical energy.

Accordingly, it is an object of this invention to provide a batterypowered explosive ignition system that can deliver energy only in apreselected energy range to fire electrically energized squibs and likefiring units such as explosive bridge wire devices.

Another object of this invention is to provide a novel electrical systemthat prevents applying too little or too much energy to fire explosivebridge wire devices or the like.

The above and other objects and features of the invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings and claims which form a part of thisspecification.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram of ablasting machine that utilizes the principles of this invention.

FIG. 2 is a schematic diagram of a preferred embodiment of the circuitryfor a blasting machine shown in FIG. 1.

DETAILED DESCRIPTION OF THE DRAWINGS Referring now to the drawings, FIG.1 illustrates a block diagram of a blasting machine which utilizes theprinciples of the invention. the basic portion of the system includes apower supply 1, an energy storage device 3, such as a capacitor forstoring energy supplied by the power supply I, a pulse generator 5 forgenerating pulses when the energy in the capacitor has reached apredetermined energy level, and a firing circuit 6 which permits thedischarge of the energy in the energy storage device 3 through the load8 which are the blasting caps or the like, when the trigger portion 7 ofthe firing circuit 6 receives pulses from the generator 5.

The power supply 1 may be either a a.c. or d.c. and include thenecessary electrical components for charging an energy storage devicesuch as a capacitor.

The energy storage device 3 is preferably a capacitor. The voltageregulator 2 may be used in electrical circuit relationship with theenergy storage device 3 to assure that the energy stored in the energystorage device 3 does not exceed a predetermined voltage level. Theenergy storage circuit may include a switch that, in the ON positionpermits the energy storage device 3 to store energy, and in the OFFposition allows the energy storage device 3 to discharge so that noenergy remains in the energy storage device 3 when the blasting machineis not in use. The charge and discharge switch 9 may be either a singleswitch or multiple switches and may also be part of the firing circuit6. 1

A voltage indicator 4 may be used in combination with the pulsegenerator 5 to produce either visual or audible signals when the pulsegenerator 5 is generating pulses.

The firing circuit 6 includes a trigger 7 which allows the energystorage device 3 to discharge into the load 8. The trigger 7 may be agaseous conductor of the threeelectrode type wherein the triggerelectrode upon receiving pulses from the pulse generator 5 allows theremaining two electrodes which are in series with the energy storagedevice 3 to conduct, thereby allowing the energy stored in the device 3to discharge into the load 8. If it is desired that the blasting machinenot be automatically triggered, a switch may be loacted in series withthe pulse generator 5 so that when the voltage indicator 4 givesindication that pulses are present, manually operating the switch toclose the contacts will cause the trigger to conduct and discharge theenergy into the load.

FIG. 2 is a schematic diagram ofa preferred embodiment of a blastingmachine that utilizes a battery and an oscillator to charge the storagecapacitor which will be discharged to fire a blasting cap or otherexplosive bridge wire device or the like. The dotted lines outliningportions of the circuitry indicate the power supply 1, the energystorage device 3, the voltage regulator circuit 2, the voltage indicator4 associated with the pulse generator, the pulse generator circuit 5,and the firing circuit 6.

The power supply 1 in this embodiment includes a battery 140, a switch9, a smoothing capacitor 130, and a transistorized oscillator circuit incombination with a step-up transformer 150, the output voltage of whichis applied to the energy storage means 3. In operation, the power supplycircuit 1 operates as follows:

A solid state switch oscillator is powered by a battery 140 or otherdirect current source. In one embodiment twelve one and one-half voltbatteries were used, which, because of the internal resistance thereof,provided a voltage between 10 to 12 volts. Connected across the battery140 is a capacitor 130 which, when charged, provides additional currentto the oscillator. A transformer 150 has its primary winding 101connected into the oscillator circuit and its secondary winding 151connected to a storage capacitor 153 through a diode 152 to store theenergy generated by the oscillator. The windings 101 and 151 oftransformer 150 are inductively coupled and wound and disposed in themanner indicated by the dots.

The solid state switch oscillator operates to intermittently interruptcurrent flow from the battery 140 through the primary winding 101 of thetransformer 150 and includes a first switching transistor 103, a firstvoltage divider network (110, 111, 112, 1 13), a second voltage dividernetwork (121, 122, 123), and first diode means (102, 104, 106) connectedbetween the first voltage divider network and the primary winding 101 ofthe transformer 150 to direct the flow of current to and from theprimary winding 101. The oscillator circuit shown is capable ofproducing oscillations in the range of 800 to 2,000 Hz.

The first voltage divider network includes a diode and a plurality ofresistors 111, 112 and 113 connected together in series across theprimary winding 101 of the transformer and the first transistor 103.

The diode means that directs the current from the primary winding 101includes a first diode 102 connected by its anode terminal to thejunction between the primary winding 101 and the first transistor 103.To permit current to flow from the primary winding 101 when transistor103 is off, diodes 104 and 106 are connected in series with one anodeterminal connected to the junction between the primary winding 101 andthe first transistor 103 and one cathode terminal connected to thejunction between the second transistor 1 l2 and the third transistor113.

The second voltage divider network includes a transistor 121, a resistor122, and a resistor 123 connected together in series across the battery140. The base of the first transistor 121 is connected, for biasingpurposes, to the junction between the diode 110 and resistor 111 of thefirst voltage divider network. The base of the first transistor 103 isconnected to the junction between resistors 122 and 123 to supply acurrent to the base of transistor 103 when the transistor 121 is in theconductive state.

The secondary winding 151 of the transformer 150 is connected to a diode152 and a capacitor 153. When the battery is l0 to l2 volts, the maximumcharge that can be obtained on capacitor 153 is about 7,000 to 8,000volts. However, voltages of this magnitude are not generally required inbattery powered explosive ignition systems, therefore, an additionalcircuit (not shown) may be added to limit the voltage across thecapacitor 153. The energy stored in the capacitor 153 is used for firingan explosive bridge wire device or the like.

In this embodiment, when a constant current source having an outputvoltage of about 10 volts is used in lieu of the battery 140 and thecapacitor 153 is a 100 microfarad capacitor, the capacitor 153 can becharged to 200 joules within [0 seconds and to 400 joules within 20seconds. Since batteries deteriorate with use, they are capable ofachieving the initial charged energy previously stated, but tests revealthat when they are used to charge the capacitor 153 to 400 joules threetimes a day for 21 days, it would take a maximum of 71 seconds of chargetime to obtain 400 joules of energy at the capacitor 153. The minimumcharge time at the end of this period to obtain 400 joules of energy atthe capacitor 153 would be 49 seconds.

The energy storage means 3 includes a blocking diode 152 and storagecapacitor 153 in circuit relationship with the secondary winding 151 ofthe transformer 150. The discharge resistor 154 allows the energystorage in capacitor 153 to be discharged when the switch 9 in the powersupply 1 is in the OFF position.

The voltage regulator 2 which prevents the voltage on the capacitor 153from exceeding a predetermined value includes a two-electrode spark gap160, a resistor 163, a capacitor 165, and a resistor 167. The functionof the regulator circuit is to drain excessive energy off the storagecapacitor 153 to prevent the storage capacitor from exceeding apredetermined upper energy limit. The spark gap 160 is a normallynonconducting device that conducts when the voltage across the devicehas reached a predetermined voltage. In this instance, the breakdownvoltage of the spark discharge device 160 is chosen to be thepredetermined upper voltage limit desired across storage capacitor 153.In operation, the voltage across the storage capacitor 153 appearsacross the spark gap 160. As the storage capacitor 153 is charged, thevoltage across the spark gap 1160 increases until the breakdown voltageof the device is reached. The spark gap 160 then breaks down andconducts current to charge capacitor 165. The current through the sparkdevice 160 decreases as capacitor 165 becomes more fully charged.Eventually the current through the spark device 160 decreases to thepoint where it no longer will support an arc in the discharge device160. The are extinguishes and spark gap 160 ceases conduction. Thecharge on the capacitor 165 is then discharged through resistor 167. Ascapacitor 165 discharges, the voltage across the spark gap device 160therefore increases, and if the voltage across the storage capacitor 153is still greater than the breakdown voltage of the spark gap dischargedevice 160, the discharge device 160 again conducts and the cycle isrepeated again. If desired, a neon indicator light could be used incombination with this circuit to give an indication when the voltageregulator is operating. The suggested method with respect to a voltageindicating device would be to place a neon indicator light and resistoracross capacitor 165 which is responsive to the charging and dischargingof capacitor 165.

The pulse generator circuit 5 includes a two-electrode spark dischargedevice 1711, resistor 171, capacitor 177, resistor 173, and resistor175. The voltage indicator light 4, such as a neon bulb, is in circuitrelationship with resistor 173 and 175 and is responsive to the chargingand discharging of capacitor 177. In operation, the two-electrode sparkdischarge device 170 will remain in a nonconducting state as long as thevoltage on the storage capacitor 153 is less than the breakdown voltageof the spark discharge device 170. When the voltage on the storagecapacitor 153 exceeds the breakdown voltage of the discharge device 170,the device conducts allowing current to pass through resistor 171 tocharge capacitor 177. As the voltage on the capacitor 177 increases, thevoltage across the spark device decreases until the spark device 170returns to the original nonconducting state. At this time, capacitor 177then discharges through resistors 173 and 175 which further applies avoltage to the neon light 4 which gives an indication that this circuitis in operation. When the voltage across the spark discharge device 170again rises to the breakdown potential of this device, conduction beginsagain and the cycle repeats itself. Each time capacitor 177 is charged,voltage is applied to neon indicator light 4 through the resistordivider network 173, 175. The neon indicator light 4 stays lit until thevoltage across the light drops below the minimum sustaining voltage ofthe light 4. By this means, each time capacitor 177 is charged, there isa visible light pulse to signal the operator that the minimum voltagehas been reached and the blasting machine may be fired. With thiscircuit, when the minimum voltage across the capacitor 153 is reachedand pulses are being generated by the pulse generator, pressing thefiring switch 181 in the firing circuit 6 will cause the pulses to betransmitted to the firing circuit.

The firing circuit 6 includes a three-electrode spark gap dischargedevice, a step-up transformer for raising the voltage of the pulsesreceived from the pulse generator 5 and applying them to the triggerelectrode of the spark discharge device 180, and a firing switch 181which permits the trigger pulses from the pulse generator 5 to betransmitted to the primary winding 185 of the step-up transformer. Forfurther details concerning the particular type of three-electrode sparkgap discharge device required for this circuit see U.S. Pats. Nos.3,187,215 entitled Spark Gap Device to I. E. Linkroum issued June 1,1965, and 3,229,146 entitled Spark Gap Device with a Control ElectrodeIntermediate the Main Electrodes to I. E. Linkroum issued Jan. 11, 1966.In operation, when the firing switch 181 is in the OFF position, nopulses are being supplied to the spark discharge gap thereby preventingthe firing of any blasting caps attached to the output terminals 190.Further, the firing switch 131 in the OFF position is yet in combinationwith the power switch 9 in the OFF position to place the dischargeresistor 154 across the storage capacitor 153 to drain any chargethereon. When the firing switch 181 is placed in the ON position, thestorage capacitor 153 will discharge if trigger pulses are present.Therefore, to discharge the energy in capacitor 153 to blasting capsattached to the output terminals 190, it is necessary that the pulsegenerator 5 is generating pulses and that the firing switch 181 is inthe ON position. When these two conditions are met, the output pulses ofthe pulse generator 5 are transmitted to the primary winding 185 of thestep-up transformer where the pulses are stepped up to a higher voltageand applied to the trigger electrode of the spark gap discharge devicethrough resistor 183 thereby causing ionization within the spark gapdischarge device and permitting current to flow through the two mainelectrodes which allows the energy storage capacitor 153 to dischargethrough the blasting caps connected to the output terminals 190. If itis desired to eliminate manual firing of the blasting caps and to havethe blasting machine discharge the energy in the capacitor 153automatically when it has reached a predetermined energy level, thefiring switch 181 may be eliminated completely. In this instance, assoon as voltage pulses are available from the pulse generator 5, thethree-electrode spark discharge device would be triggered to dischargethe energy in the capacitor 153 through the blasting caps (not shown)connected to the terminals 190.

OPERATION Referring now to FIG. 2, the circuit operates as follows: Whenswitch 9 is in the OFF position, resistor 154 removes the energy storedin capacitor 153. When switch 9 is closed, resistor 154 is removed fromthe eircuit and current flows from the battery 140 through capacitor 130and through transistor 121, resistor 122 and resistor 123. Accordingly,a voltage is applied across the voltage divider network containingtransistor 121 and the voltage dividing network containing diode 110.Since there is a positive voltage applied across the emitter basecircuit of the transistor 121, the transistor 121 conducts permitting acurrent to flow through resistors 122 and 123 and through lead 124 tothe base of transistor 103 which is in the nonconducting state. When thecurrent to the base of transistor 103 is sufficient, transistor 103conducts (ON). When the transistor 103 conducts, current flows throughthe transformer primary winding 101 and transistor 103. With currentflowing to ground through the primary winding 101, transistor 121 beginsto return to the nonconductive (OFF) state as the base to emittercurrent of that transistor begins to decrease. Eventually transistor 121becomes nonconductive, removing the necessary base current to transistor103 which also becomes nonconductive (OFF). Once the transistor 131turns OFF, the electrical energy stored in the primary winding 101during the ON or conduction period of transistor 131 is removed ascurrent leaves the primary winding 131 and flows through diodes 104,106, 110 and resistors 111 and 112. This action also operates to backbias transistor 121 so that it remains in the nonconductive state.Further, since during this time the rate of change of current withrespect to time (di/dt) becomes sharply negative the voltage inducedacross the secondary winding 151 for this period also reverses and thesecondary winding 151 becomes a current source. Therefore, during thetime di/dt is negative, most of the energy stored in the primary windingof the transformer is transferred to the secondary winding 151 in amanner that allows the diode 152 to conduct and to supply energy to thecapacitor 153 and to supply energy to the capacitor 153 and to a load(not shown). Thus, electrical energy which is fed to the primary windingduring the conducting period of transistor 103 is transferred to thecapacitor 153 during the nonconducting period of transistor 103. Theentire action is cyclic for as the energy is removed from thetransformer 150 the reverse bias on transistor 121 is removed allowingtransistors 121 and 103 to turn ON and repeat the entire operationagain. (About 800 to 2,000 112.)

As the energy stored in the capacitor reaches a predetermined level, thepulse generating circuit begins generating trigger pulses. This occurswhen the spark gap discharge device 170 reaches its breakdown potential.To assure that the energy stored in the capacitor is above thepredetermined energy level but not in excess of a second and higherenergy level, a voltage regulator circuit 2 is utilized. This eliminatesexcessive energy levels that cause adverse operation of the blastingmachine.

Once the trigger pulses are present and the energy stored in thecapacitor is within a preferred range depressing the firing switch 181applies trigger pulses to transformers 182 which causes spark gap device180 to conduct, thereby allowing the energy in capacitor 153 todischarge into the blasting caps (not shown) attached to the outputs 190and detonate explosives.

3300 microfarad, 30 Volts d.c.

0.45 to 0.61 microfarad 3KV 0.008 to 0.012 microfarad,

400 microfarad 2.5KV

0.025 to 0.03 microfarad 3KV Capacitor Capacitor Capacitor 177 Capacitor153 Capacitor 187 Resistor 122 6.2 ohms, 11W

Resistor 123 33 ohms AW Resistor 111 100 ohms 2W Resistor 112 1000 ohms,AW

Resistor 113 10K ohms AW Resistor 154 SR ohms 10W Resistor 167 20K ohms20W (2 in series) Resistor 163 2 ohms 20W (2 in parallel) Resistor 1750.33 megohms 2W Resistor 173 1.36 megohms 4W (2 in series) Resistor 171500 ohms 10W Resistor 186 20 megohms 1W Resistor 183 1K ohms 5W Resistor189 10K ohms 10W Transistor 121 Type MJE 341 Transistor 103 Type 2N3055Beta 20-35 Diodes 110, 102, 104, 106 GE A14F Diode 152 Motorola MR 995A2200 volts d.c. (breakdown)- Bendix Corp. Sidney, N.Y. Part no.10-374105-21 2000 volts d.c. (breakdown)- Bendix Corp. Sidney, N.Y. Partno.10-374121-14 Discharge Device 160 Discharge Device Transformer 150Transformer 182 Switch 9 and 181 While a preferred embodiment of theinvention has been disclosed, it will be apparent to those skilled inthe art that changes may be made to the invention as set forth in theappended claims, and in some cases, certain features of the inventionmay be used to advantage without corresponding use of other features.For example, different types of semi-conductors, or solid state controldevices may be substituted for the types illustrated. Accordingly, it isintended that the illustrative and descriptive materials herein be usedto illustrate the principles of the invention and not to limit the scopethereof.

Having described the invention what is claimed is:

1. A blasting machine for initiating electro-explosive devices whichcomprises:

means for storing electrical energy, said storage means having twooutput terminals;

means for supplying electrical energy to said energy storage means;

means for producing a plurality of electrical pulses when said energystorage means has reached a first predetermined energy level, said meansfor producing electrical pulses including a second normallynonconductive gaseous conductor which is rendered conductive when apredetermined voltage is applied thereto and a resistor-capacitorcircuit in series with said second gaseous conductor so that when saidsecond gaseous conductor is rendered conductive, said capacitor lowersthe voltage applied to said second gaseous conductor to a voltage belowsaid predetermined value and said second gaseous conductor is renderednonconductive;

switching means for receiving said pulses, said switching means operableto permit the discharge of said energy storage means only during thepresence of said pulses, whereby said energy storage means cannot bedischarged below said predetermined energy level, said switching meansincluding a first normally nonconductive gaseous conductor having oneelectrode connected to one output terminalof said energy storage means,a second electrode, and a trigger electrode connected through saidswitching means to said pulse means, said first gaseous conductor beingrendered conductive upon receiving said pulses at said trigger electrodewhen said switching means is closed whereby when pulses from said pulsemeans are transmitted to said first gaseous conductor, said firstgaseous conductor is rendered conductive to permit said storage means todischarge, and a switch connected between said first gaseous conductorand said pulse means, said switch operable in the ON position to permitthe passage of said pulses to said first gaseous conductor whereby saidenergystorage means is discharged only when said switch is in the ONposition and when said pulse means is producing pulses;

means for preventing said means forstoring electrical energy fromexceeding a second predetermined energy level which is above said firstpredetermined energy level whereby said energy storage means isprevented from reaching energy levels above said second predeterminedenergy level; and

means for connecting the second electrode of said first gaseousconductor, and the other output terminal of said storage means to acircuit containing an electro-explosive device whereby saidelectroexplosive device is exploded upon conduction of said firstgaseous conductor and the closing of said switching meanswhich permitsthe discharge of said energy storage means.

2. The blasting machine as described in claim 1 wherein said means forpreventing said means for storing electrical energy from exceeding asecond predetermined voltage level includes an electrical circuit whichcomprises:

a third gaseous conductor connected in series to a resistor and acapacitor, said capacitor connected in parallel with a second resistor,said electrical circuit connected across said means for storingelectrical energy whereby when said means for storing electrical energyreaches said second predetermined energy level said third gaseousconductor conducts to prevent said means for storing electrical energyfrom exceeding said second predetermined energy level.

1. A blasting machine for initiating electro-explosive devices whichcomprises: means for storing electrical energy, said storage meansHaving two output terminals; means for supplying electrical energy tosaid energy storage means; means for producing a plurality of electricalpulses when said energy storage means has reached a first predeterminedenergy level, said means for producing electrical pulses including asecond normally nonconductive gaseous conductor which is renderedconductive when a predetermined voltage is applied thereto and aresistor-capacitor circuit in series with said second gaseous conductorso that when said second gaseous conductor is rendered conductive, saidcapacitor lowers the voltage applied to said second gaseous conductor toa voltage below said predetermined value and said second gaseousconductor is rendered nonconductive; switching means for receiving saidpulses, said switching means operable to permit the discharge of saidenergy storage means only during the presence of said pulses, wherebysaid energy storage means cannot be discharged below said predeterminedenergy level, said switching means including a first normallynonconductive gaseous conductor having one electrode connected to oneoutput terminal of said energy storage means, a second electrode, and atrigger electrode connected through said switching means to said pulsemeans, said first gaseous conductor being rendered conductive uponreceiving said pulses at said trigger electrode when said switchingmeans is closed whereby when pulses from said pulse means aretransmitted to said first gaseous conductor, said first gaseousconductor is rendered conductive to permit said storage means todischarge, and a switch connected between said first gaseous conductorand said pulse means, said switch operable in the ON position to permitthe passage of said pulses to said first gaseous conductor whereby saidenergy storage means is discharged only when said switch is in the ONposition and when said pulse means is producing pulses; means forpreventing said means for storing electrical energy from exceeding asecond predetermined energy level which is above said firstpredetermined energy level whereby said energy storage means isprevented from reaching energy levels above said second predeterminedenergy level; and means for connecting the second electrode of saidfirst gaseous conductor and the other output terminal of said storagemeans to a circuit containing an electro-explosive device whereby saidelectro-explosive device is exploded upon conduction of said firstgaseous conductor and the closing of said switching means which permitsthe discharge of said energy storage means.
 2. The blasting machine asdescribed in claim 1 wherein said means for preventing said means forstoring electrical energy from exceeding a second predetermined voltagelevel includes an electrical circuit which comprises: a third gaseousconductor connected in series to a resistor and a capacitor, saidcapacitor connected in parallel with a second resistor, said electricalcircuit connected across said means for storing electrical energywhereby when said means for storing electrical energy reaches saidsecond predetermined energy level said third gaseous conductor conductsto prevent said means for storing electrical energy from exceeding saidsecond predetermined energy level.